Silicon carbide (SiC) bipolar junction transistors (BJTs) are high-performance power devices having low on-state and switching losses and are also capable of high-temperature operation thanks to the high breakdown electric field, high thermal conductivity and high saturated drift velocity of electrons in SiC. SiC is a wide bandgap semiconductor and may advantageously be used for manufacturing devices for high power, high temperature and high frequency applications.
In a high power bipolar junction transistor (BJT) comprising a collector region, a base region and an emitter region, the critical characteristics representative of the performance of the BJT are the common emitter current gain, the specific on-resistance and the breakdown voltage. For a specific doping concentration, the base region of the BJT is preferably as thin as possible in order to obtain a high current gain. However, the minimum thickness of the base region is limited by the base punch-through effect, which represents total depletion of the base region at a high collector bias. Referring to the doping of the base layer, on the one hand, a high breakdown field requires a high doping level in the base region of the BJT in order to prevent early punch-through while, on the other hand, a high doping level in the base region decreases the emitter current gain, which is a disadvantage in practical application. A drawback of prior art SiC BJTs is therefore that they do not simultaneously provide a sufficiently high emitter current gain and a sufficiently high blocking voltage.
Yet another limitation of SiC bipolar technology originates from surface recombination which limits the achievable emitter current gain. Further, surface recombination is a potential stability issue, as the interface properties might degrade with time under the conditions of minority carrier injection.
Thus, there is a need for providing new designs of SiC BJTs and new methods of manufacturing such BJTs that would alleviate at least some of the above-mentioned drawbacks.